에너지공학, 제23 권 제 3 호 (2014) Journal of Energy Engineering , Vol. 23, No. 3, pp. 1~6 (2014) http://dx.doi.org/10.5855/ENERGY.2014.23.3.001 A STUDY ON THE ENGINE PERFORMANCE OF A SPARK IGNITION ENGINE ACCORDING TO THE IGNITION ENERGY Sung Bin Han 悯 Department of Mechanical & Automotive Engineering, Induk University (Received 12 May 2014, Revised 16 June 2014, Accepted 18 June 2014) Abstract The more or less homogeneous fuel-air mixture that exists at the end of the compression process is ignited by an electric ignition spark from a spark plug shortly before top dead center. The actual moment of ignition is an optimization parameter; it is adapted to the engine operation so that an optimum combustion process is obtained. Brake mean effective pressure (BMEP) of the spark ignition energy control device (IECD) than conventional spark system at the stoichiometric mixture is increased about 9%. For lean burn engine, the lean limit is extended about 25% by using the IECD. It was considered the stability of combustion by the increase of flame kernel according to the high ignition energy supplies in initial period and discharge energy period lengthen by using the IECD. Key words : Engine performance, Brake mean effective pressure (BMEP), ignition energy control device (IECD), Lean limit 1. INTRODUCTION problem of land transportation in the future [1]. A number of automobiles on the market obtain The development of automobiles with heat high fuel efficiency by the use of lean-burn engines is one of the greatest achievements of engines. By using a stratified charge, these engines modern technology. However, the highly developed obtain efficient combustion with overall air-fuel automotive industry and the large number of ratios of 21. Figure 9-7 shows that normal catalytic automobiles in use around the world have caused converters will work in reducing HC and CO at and are still causing serious problems for society lean conditions but are very inefficient at reducing and human life. Deterioration in air quality, global NOx. Special converters, which use platinum and warming, and a decrease in petroleum resources are rhodium combined with alkaline rare earths, have becoming the major threats to human beings. More been developed for lean-burn engines. Combustion and more stringent emissions and fuel consumption temperatures must be limited in these engines so regulations are stimulating an interest in the that NOx production is kept within manageable development of safe, clean, and high-efficiency limits [2]. transportation. To increase operational reliability, ignition It has been well recognized that electric, hybrid systems should have low source impedance and/or a electric, and fuel cell-powered drive train fast voltage rise (shunt resistance). Furthermore, technologies are the most promising solutions to the ignition systems must provide sufficiently high voltage. In future ignition systems, we can 悯 To whom corresponding should be addressed. anticipate a further rise in the demands on available Department of Mechanical & Automotive Engineering, Induk University 12 Choansan-ro, Nowon-gu, Seoul 139-749, Rep of Korea. voltage. In particular, the required ignition voltage Tel : TEL:+82-2-950-7545 E-mail : [email protected] in a lean-running engine with direct fuel injection 2 Sung Bin Han under a partial load in stratified-charge operation is discharge circuit of Randeberg et al., and concluded higher than for a comparable engine in that, due to the hidden subtle energy supply, the stoichiometric operation since the charge dilution real spark energies in the experiments were from excess air and/or exhaust recycling increases significantly larger than those quoted in the the gas density in the cylinder and, hence, raises published paper. The additional energy in the the breakdown voltage at the time of ignition [3]. discharge was of the order of 1 mJ. With the aim In spark-ignition engines, the electrical discharge to minimize the additional energy, an improved produced between the spark plug electrodes by the version of the Randeberg et al. spark generator was ignition system starts the combustion process close constructed, which reduced the additional energy to the end of the compression stroke. The input to the order of 0.25 mJ . high-temperature plasma kernel created by the spark The spark forming at the spark plug can be develops into a self-sustaining and propagating divided into three sequential types of discharge with flame front. The function of the ignition system is very different to initiate this flame propagation process, in a energy and plasma physical properties. Initially, repeatable manner cycle-by-cycle, over the full load the voltage at the spark plug rises sharply. As soon and speed range of the engine at the appropriate as the current charge forming in the field reaches point in the engine cycle [4]. the opposing electrode, breakdown occurs within a Understanding of flame initiation is important not few nanoseconds. The impedance of the electrode only for fundamental combustion research but also path falls drastically, and the current rises quickly for fire safety control and the development of from the discharge of the leakage capacitance of the low-emission gasoline and homogeneous charge spark plug [3]. compression ignition (HCCI) engines. When an In a conventional spark-ignition engine the fuel external energy is locally deposited into a and air are mixed together in the intake system, combustible mixture, there are four possible inducted through the intake valve into the cylinder, outcomes: an evolution from outwardly propagating where mixing with residual gas takes place, and spherical flame to planar flame; a stationary flame then compressed. Under normal operating ball; a propagating self-extinguishing flame; or a conditions, combustion is initiated towards the end decaying ignition kernel. The evolution of the flame of the compression stroke at the spark plug by an kernel and the final outcome depends on the electric discharge. Following inflammation, a magnitude of energy addition, fuel concentration, turbulent flame develops, propagates through this radiation heat loss and transport and kinetic essentially premixed fuel, air, burned gas mixture properties. Efficient flame initiation with minimum until it reaches the combustion chamber walls, and energy deposition and successful control of fire then extinguishes [4]. This paper investigates the spreading highly depend on the understanding of effect of performance from a spark ignition engine the correlations between ignition kernels, flame according to the multi spark ignition energy control balls, self-extinguishing flames and propagating device. spherical and planar flames, as well as the impacts of radiation intensity and the transport properties on 2. EXPERIMENTAL SETUP AND the flame regime transitions [5-7]. EXPERIMENTS Randeberg et al.[8] described a spark generator for producing synchronized capacitive spark Figure 1 shows the block diagram of the ignition discharges of low energy, down to below 0.1 mJ. energy control device (IECD). The IECD was However, Eckhoff et al. [9] re-examined the consisted of a capacitor discharge igniter, charge 에너지공학 제23 권 제 3 호 2014 A STUDY ON THE ENGINE PERFORMANCE OF A SPARK IGNITION ENGINE ACCORDING TO THE IGNITION ENERGY 3 Fig. 1. Block diagram of the ignition energy control Fig. 2. Discharge energy versus number of spark. device (IECD). 30A) that could discharge the ignition energy of Table 1. Spark duration, spark energy and discharge pattern of spark energy of IECD. condenser by trigger pulse. And the ignition coil used was that a conventional spark ignition engine Spark Cap. Ind. Total No.of used [10]. The energy is charged in a capacitor interval, energy, energy, energy, spark ms mJ mJ mJ discharge igniter that copes with the high speed Single 1 2.67 0.51 3.18 revolutions, in addition to the followings is that a 0.15 2 13.01 0.77 13.77 charge discharge control circuit that to spark with 0.15 4 14.58 1.67 16.25 the required spark interval and times in spark 0.15 6 14.58 3.07 17.65 0.15 8 14.58 4.84 19.42 timing. Single 1 2.67 0.51 3.18 The IECD converts the 12V to the high voltage 0.20 2 13.01 0.98 13.98 AC, and charges energy in condenser, and 0.20 4 15.40 2.54 17.94 discharges in any time. At this time, the noise 0.20 6 15.40 4.98 20.38 0.20 8 15.40 7.52 22.92 occurred by the supplied high voltage in condenser. Single 1 2.67 0.51 3.18 The noise operates on the SCR, and has become to 0.25 2 13.01 1.63 14.63 break the igniter as well as the control is imperfect. 0.25 4 16.25 3.66 19.90 0.25 6 16.25 7.34 23.59 To solve these problems, it was selected the low 0.25 8 16.25 12.08 28.32 voltage type. The charge control circuit consists of wave shaping circuit, multi signal circuit, time control circuit and discharge control circuit. The retarder, and flip-flop circuit. The wave shaping capacitor discharge igniter was parallel connected circuit inputs discharge control circuit and sparks by with the capacitor discharge igniter as much as the input of SCR trigger of the capacitor discharge number of ignited spark. The charge control circuit igniter. The simultaneously input signal in time supplied spark energy to the capacitor discharge retarder delays the time, 12 DC voltage supplies to igniter, and a discharge control unit supplied energy DC-AC converter by multi signal circuit and of the required spark interval and times in spark flip-flop circuit, and then occurs an alternating timing.